[Bug libstdc++/26907] New: Two times filebuf::sungetc() at beginning of file gives undefined result

["trumsko at yahoo dot com" <gcc-bugzilla at gcc dot gnu dot org>]

If I use filebuf::sungetc() at the beginning of a file, the result of the next
sbumc() call is not
allways the first character in the file:


#include <fstream>
#include <iostream>

using namespace std;
int main()
{
  ifstream infile("test.dat");
  filebuf* inbuf=infile.rdbuf();
  int res;

//at beginning of file
  res=inbuf->sungetc();
  res=inbuf->sungetc();

  res = inbuf->sbumpc();
  if ( res == EOF )
    cout << "x" << endl;
  else
    cout <<(char) res << endl;
  res=inbuf->sungetc();

//at beginning on file
  res=inbuf->sungetc();
  res=inbuf->sungetc();

  res = inbuf->sbumpc();
 if ( res == EOF )
    cout << "x" << endl;
  else
    cout <<(char) res <<"-"<<res<< endl;

}


The first sbumpc returns the first character in the file, the second doesn't. I
don't think that it is intended,
that I have to do the bookkeeping about the number of sungetc() calls manually,
to guarantee, that the sungetc()
acts in a defined way.
Cheer, Troban


-- 
           Summary: Two times filebuf::sungetc() at beginning of file gives
                    undefined result
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: trumsko at yahoo dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26907